for the degree of Master of Philosophy at The University of Hong Kong in September 2003

In this study, the differences in protein profiles between the anthers of a genic thermo sensitive male sterile rice mutant (AN S-l) and its wild type (AN-N) were displayed in classical two dimensional (2DE) electrophoresis gels; and tryptic fragments fingerprinting in MALDI- TOF Mass spectroscopy (MS) was employed to identify the proteins that showed differential expression. Since the comparison was made at the late stage of anther development, the differences may reveal those differentially expressed proteins (mostly down-regulated in the mutant) which possibly playa role in normal anther development.

As the temperature inducing male sterility was at 31? for the AN S-l mutant, plant materials were grown according to the following conditions: wild type at 31? (AN-N 31), AN S-l either at 24? (AN S-l 24) or at 31? (AN S-l 31). Four hundred micrograms of anther protein extracts were loaded for isoelectric focusing and at least six 2DE experiments were conducted for each growing condition. On 2-D gels, AN S-l 31 protein samples showed a general mild degradation profile when compared with samples

from both AN-N 31 and AN S-l 24, indicating that high temperature might play an important role in rice male sterility.

In this study, a detailed comparison of protein patterns between AN-N 31 and AN S-l 31 was made. It was found that 446 protein spots were regarded as significant changes in expression level (> 2 folds) between AN-N 31 and male sterile AN S-l 31. Among which 60 protein spots were investigated and 31 protein spots were identified successfully. The down-regulated proteins found in the AN S-l 31 include those involved in hydrogen peroxide detoxification, protein folding maintenance, A TP synthesis, carbohydrate metabolism, cytoskeleton formation and starch synthesis. However, the level of transcripts encoding these proteins did not necessarily show down-regulation in Northern blotting.

These results seem to suggest that the accumulation of cytosolic hydrogen peroxide might impair A TP synthesis in anthers of the AN S-l 31; the subsequent low energy status thereby cannot fulfill the energy demand for anther development and eventually wi11lead to pollen abortion. This study points to the possibility of hydrogen peroxide involvement in male sterility in AN S-l mutants. (359 words)